The invention relates to filter assemblies used to filter liquids circulating in internal combustion engines or hydraulic equipment.
The above filter assemblies are made up of a filter body within which a filter cartridge is set, generally with a cylindrical shape and which includes a filtration medium which can for example be made of paper, cardboard or felt or other material. This medium is limited by two end flanges.
The present trend is to produce such filter cartridges in materials which can be incinerated. In particular, as far as the flanges are concerned, the present trend is to produce the flanges in plastic material.
It is to be noted that in many cases, it is preferable to envisage two circuits for the liquid to be filtered, that is a main circuit and a branch circuit making it possible to remove both larger and smaller particulates during filtering of the liquid passing through in the main circuit. However, in such a case, generally only one filter cartridge is used, the latter then being constituted of two essential parts integrating two filtration media, one for treating the liquid in the main circuit and the other for filtering the liquid in the branch circuit. The filter medium used for filtering the liquid in the branch circuit is, in the present state of the art, constituted by a stack of paper or cardboard disks showing a central aperture and able to be of circular, hexagonal, octagonal or other shape. (The term xe2x80x9cdisk stackxe2x80x9d used in the present patent application is aimed at covering any laminate structure constituted by superposition of several layers of filter medium in paper, cardboard or any other equivalent material, for example synthetic or inorganic fibers, able to take any geometric shape). The disks constituting the stack in question include one or several holes and form a column showing a central aperture.
A problem encountered with this type of filter medium comes from the fact that the height of the stack diminishes little by little with time. In fact, in order to avoid a radial passage of the fluid to be filtered in such a stack, which would lower the quality of filtration, it is necessary to compress said stack in such a way as to ensure permanent and good cohesion of the disks constituting it. To this end, filter assemblies using such a cartridge with a double filter medium are generally provided with a spring set between the cover and said cartridge, making it possible to press the latter onto the base of the chamber and to compress the disk stack.
As a complement to the use of such a spring, it has also been envisaged to provide external arms around this stack operating together with a lower flange, said arms being provided with ratchets which engage the flange and allow the cohesion of the disks to be maintained when the height of the stack diminishes under the effect of pressure. Such a technique is described in U.S. Pat. No. 5,665,231.
Such prior art, however, presents many inconveniences. In the first place, it can be noted that the device described is relatively complex to produce. Moreover, in certain cases, it does not prevent the disks constituting the stack to turn on themselves, which contributes to deterioration of the quality of filtration. Finally, it still requires the use of a compression spring which raises the cost of fabrication of the filter assembly and complicates changing the cartridge.
The principal objective of the present invention is to propose a device for maintaining a disk stack used in a branch filter which does not have the inconveniences of the present state of the art.
A particular objective of the present invention is to propose such a maintaining device which can make it possible to be free from using a compression spring for the cartridge in the chamber.
A further objective of the present invention is to propose a cartridge equipped with such a branch device which can be integrated easily on a cartridge with a double filter medium.
Another objective of the present invention is to propose a cartridge equipped with such a maintaining device allowing it to be removed cleanly from the chamber of the filter assembly.
A further objective of the present invention is to propose such a maintaining device which also makes it possible to centre the disks constituting the stack and to index them.
These different objectives are attained pursuant to the present invention by a maintaining device for a filter medium comprising a stack of filtration disks with a central aperture characterised in that the maintenence device includes a first flange presenting at least one central aperture, a second flange, and at least one first central element which is perforated and intended to operate together with said central aperture of said stack of filtration disks, said first central element being integral at one of its ends with said second flange and being provided at its other end with ratchets intended to operate together with said central opening of said first flange.
In relation to the present state of the art, the present invention proposes envisaging a ratchet mechanism which is not external to the disk stack but inside it. Such a characteristic makes it possible to ensure higher sturdiness for the maintaining device and does not hinder filtration.
It is to be noted that to allow the passage of filtered fluid from the outside of the stack to its central aperture the central element must necessarily be perforated. It is evidently possible to envisage different architectures to allow the passage of this fluid into the central aperture.
According to a preferred variant, this first central element has a first part with an essentially solid cross-section and a second part constituted of a plurality of lugs provided with ratchets. One could envisage a number of lugs provided with ratchets and a shape for the first part which could vary according to the shape of the central aperture of the disk stack. In fact, according to the modes of embodiment, this central aperture could present a variable shape (circular, oblong, hexagonal, octagonal etc.).
Preferably, said first flange has as many central openings as said first central element has lugs provided with ratchets, each lug operating together with one of said central openings.
According to one interesting embodiment of the invention, the second part of the first central element can be constituted of four lugs provided with ratchets. Also according to an interesting embodiment of the invention, the first part of this central element will present a non-circular cross-section in such a way as to operate together with a disk stack whose central aperture is not circular. In this way, it will be possible to index the centring easily for the disk stack around the central element.
Again, according to a preferred variant, the central element is formed as a single block with the second flange. Such a characteristic allows the fabrication costs of the maintaining device according to the invention to be reduced.
According to the invention described above, the maintaining device can thus be constituted of two flanges, and a central ratchet element. During the use of such a device, the stacking of disks will be piled on the central element and blocked between the two flanges, making this central element operate together with the openings of the first flange. During the creep of the filter medium resulting in a reduction of the height of the disk stack, the second flange comes closer to the first flange under the effect of the pressure of fluid to be filtered and/or possibly a spring positioned in the filter assembly to hold down the cartridge in the chamber; the closing of the second flange towards the first flange is due to the operation of the ratchets together with the openings of this first flange.
According to a preferred embodiment of the invention, the maintaining device according to this is not made up of two flanges, that is a fixed flange and a mobile flange, but three flanges, that is a first fixed flange then a second intermediary mobile flange and then a third fixed flange. In this case, the first central element is preferably hollow and the device will comprise a third flange and a second central element integral at one of its ends with said first flange and at the other of its ends with said third flange, said second central element having a cross-section smaller than said first central element and sliding inside it.
In this case, a joint will be set between the first central element and said second element to stop any leak of the filtered fluid.
According to a preferred embodiment, the second central element will be formed in a single block with the third flange.
The ratchets described above arranged around the first central element will moreover be advantageously placed at a height xe2x80x9chxe2x80x9d corresponding to about 10 to 20% of the initial height xe2x80x9cHxe2x80x9d of the stack of filtration disks.
The invention also relates to any filter cartridge characterised in that it presents a filter medium constituted by a stack of filtration disks with a central aperture and a maintaining device as described above, said first central element of this extending into said central aperture of said stack.
Preferably, such a cartridge integrates a second filter medium defined by an upper flange and a lower flange, said upper flange being constituted by said first flange of said maintaining device.
Finally, the invention also relates to a filter assembly comprising a filter body constituted of a chamber and a cover, and a cartridge such as that described above, said cartridge designed to be disposable after use, characterised in that said cover has an internal peripheral edge designed to operate together with a flange of said cartridge in such a way as to extract said cartridge when the chamber cover is removed.
Preferably, said filter assembly does not include any spring to hold the cartridge down in the chamber and compress the disk stack.